Magneto-strictive sound generator



June 25, 1935.

Filed Dec 15, 1932 3 Sheets-Sheet 1 INVENTOR Ha rm? 6. Han es ATTORNEY June 25, 1935. q HAYES MAGNETO sTRIcTIvB SOUND GENERATOR 3 Sheets-Sheet 2v Filed Dec 15, 1932 nvvsuron Ham e C. Ha e5 BY j ATTORNEY Jun 25, 1935. H. c. HAYES KAGNE'i'O STRICTIVE SOUND GENERATOR Filed Dec. 15, 1932 3 Sheets-Sheet 3 a H N Patented June 25, 1935 (Granted under the act of March '3, 1883.2; a

amended April 1928; 370 O. G. 757) This invention relates to a device for generat-' ing directional sound signals and has among vibrating member.

its Objects to face of hate in phase. will have no nodal lines and will permit of utilizing in a single directed beam the sound energy generated onboth sides of the provide a sound generating sur- Another object is to provide a device of the type mentioned having higher acoustical efilciency, lower cost of manufacture and which will be simpler and less expensive to operate than more fully hereinafter.

and the vtotal'energy (E) radiated into the devices of this type heretofore known.' I

With the above and other objects in view, the invention consists in the construction, com ination and arrangement of parts as will be des ribed In the drawings: t

Fig. 1 is an axial section of one form of my invention adapted to give a small angle conical beam of sound;

Fig. 2 is a perspective view of the same with parts broken away;

- Fig. 3 is an axial section of my invention modifled to a disk;

Fig.- 4 shows diagrammatically the nature of the sound field around the vibrating cylinder;

Fig. 5 illustrates the use of a cylindrical mirror to project the sound beam as in a fog signal;

Figs. 6 and 7 are respectively an axial section and a trans erse sectionof a form of my invention where n only the sound generated at the outer surface of the cylinder is utilized;

Fig. 8 is a schematic diagram of the circuits involved in the operation of my invention.

The sound energy (dE) which a vibrating body radiates into the surrounding mediumper second from an increment of surface is proportional to the area (dS') ofthat increment, to c the square of the amplitude through which it vibrates and to n, the square of the pitch or frequency of vibration. Expressed mathematically,

this statement,becomes:

' dE dSahn v (1) medium per second will be equal to .the summation of the (d E) over the whole area of contact between the vibrating medium. Such a summation will be in the nature of:

E ==S.a=.n'* (2) where (E) represents the rate of generatlonof sound energy in the medium, (8) the area of the any desired area all of which will vi-' ing this point from each project the sound beam in the form of body andthe surrounding' OFFlCE is not quite so obvious that this is not the only,

or even most dependable, criterion. for evaluating a sound generator because there is no indicated evaluation regarding the intensity of sound energy that will be supplied to distant points in the medium, 1. e., no account is taken of the distribution of the sound energy in the medium.

The sound energy received at any point inthe medium is the vector sum of the energy reachand all of the increment areas of the generating surface. It is apparent that .unless the phase relations existing-among the surface increments is such that the sound energy transmitted therefrom is vectorially additive, the sound energy received at a point will not have the maximum attainable value due to the annulment of part of the sound energy through interference.

Vibrating bodies in general break up into stand ing wave systems and under such conditions the surface is separated into nodes and loops, an example of which is the well known Chladnis figures associated with vibrating plates. The average difference in phase of vibration of areas ad- ,jacent to and separated by a nodal line is onestantially the same amount of sound energy but;

differs in phase by 180 degrees for the reason that-when the surface on one side of the plate moves toward the medium to produce acompression, the area directly away from the medium and creates a rarefaction. Thus'the sound energy generated on one side of the diaphragm is at any and every instant 180 degrees out of phase with that generated on the opposite side and therefore a vibrating plate does not in general make a effective sound generator. In known devices e ploying a vibrating diaphragm, the area must be kept smallvand a baflle of some sort used to cut off the sound generated' on one side to prevent interferencewith,

that produced on the other.

opposite is moving dia hragm are or in parallel but of the coil to the edge over the sound generating area and for the same reason only one side thereof can be used. The

only 'way the power of such a device can be made large is by increasing the factor (a), the amplitude of scillation of the sound generating surface, in other words, by driving the diaphragm harder. But this procedure cannot be pushed far for the reason that in a liquid medium cavitation takes place, i. e., the diaphragm pulls away from the medium thereby leaving a partial vacuum. In the case of a gaseous medium, the ratio of elasticity to density is a function of the pressure and temperature, sufllcient difference in this ratio occurs between the compression and rarefaction portions of the waves to cause an appreciable difference in the velocity of propagation of the different portions thereof. The loss of energy of such sound waves during propagation is excessive so that the extra power required at the source to generate sound waves of abnormally high amplitudes are soon lost during transit due to the difierence in velocity of the compressional and rarefactional portions of the sound waves. It is therefore apparent that some means other than a diaphragm must be employed to generate powerful sound signals. The present invention provides such a means.

In Fig. 1 the cylinder ID of magneto-strictive material is positioned between rings II and i2 by means of flexible supporting elements IS. The rings II and I2 are preferably of insulating material and are retained in operative relation by straps l4 connected to both of the rings. A plurality of coils I5 of wire are disposed'around cylinder ill substantially in the form of a toroid, that is, they extend longitudinally of the cyl' inder and each coil lies both inside and outside of its portion of the wall of cylinder In. These coils are all connected together either in series the connection must be such that the magnetic field of each coil will be additive with that of the coils adjacent thereto. It is apparent that if the coils were made continuous over the surface of cylinder ill, the sound energy generated by the cylinder would be greatly diminished by and therefore the coils-are spaced apart to leave free areas for the passage of the sound energy.

The spaces between the coils are preferably of substantially the same width as that of the coils, which should be not greater than a half wave length of the sound in the transmitting medium and preferably somewhat nearer to a quarter wave length. The width of the coils shouldbe kept small with respect to the wave length for the reason that sound generated by cylinder ill on the areas covered by the coils passes out between the surfaces of the cylinder and the coil to mix with the sound generated'by the areas not so covered; and in order'for these sound increments to add effectively, the distance from the center of the adjacent gaps should be small in comparison with a wave length. When the current in the coils l5 fluctuates periodically, the magnetic field about the cylinder III is varied and due to the magneto-strictive effect the :cylinder is caused to vibrate radially, that is, it expands-end contracts in synchronism with the changes in the magnetic field. This radial vibration of the cylinder sets'upsou'nd waves that where passing through the coil system- 2,oo5,741 T eration. of energy is secured if the frequency of the current used is the same as the natural recs nant frequency of cylinder Iii. I

A trough-shaped annular member 16 having outwardly flaring edges 61 and I8 is secured to ring it. A conical reflecting member is having an apical angle of degrees is mounted on outturned edge It to be concentric with cylinder 19 and has an altitude equal to the length of the cylinder. A frusto-conical reflector 26 is carried by out-turned edge W and is also concentric with cylinder In and has an altitude equal to the length of the cylinder. The slope of the wall of these reflectors with respect to their axes is 45 degrees. The spacing of reflector 20 from cylinder It is such that at any point thereof its distance from the cylinder is one-half wave length greater than the distance from cylinder iii to reflector It along the same line. The wave length used as the basis of this measurement is that of sound having the same frequency as the resonant frequency of cyl-;

inder Ill when it executes pure radial vibrations. This is given very approximately as the quotient of the velocity of sound in the material of which the cylinder is made divided by. its circumference;

Since the surfaces of reflectors i8 and 28 make angles of 45 degrees with the elements of cylinder Ill, it follows that sound generated by any increment of the cylinder will have its direction of propagation changed by 90 degrees upon reflection at points such as 2| on the outer reflector and 22 on the inner reflector, and therefore all the sound generated by both surfaces of the cylinder will be directed parallel to the common axis of the cylinder and the cones. At every instant the sound waves from the inner surface of the cylinder differ in phase by one-half wave length from those originating on the directly opposite increment of the outer face of the cylinder and since the distance from the cylinder to the outer reflector is one-half wave length greater than the distance of a corresponding point of the inner reflector therefrom, the waves from the outer surface are brought into phase with those from the inner one. Thus the phase relations and character of the sound beam will be practicallyidentical with one that would be given by a circular diaphragm having a diameter equal to the maximum diameter of reflector 20 whereof the whole area oscillates in phase. It is well known. that such a sound generator produces a conical sound beam wherein (0), the half angle of the. beam, bears the following relation to (w) the wave length of the sound in the medium, and to (d)- the diameter of the diaphragm:

0= k sine"'% a where (k) is a constant of proportionality of value approaching unity.

The form of my invention shown in Fig. 3 adds to the structure of Figs. 1 and 2 a second conical reflector 23. disposed coaxially with reflector I! and with its apex turned toward and adjacent the apex of reflector I9. The bone 23 deflects the sound beam outwardly in a radial direction which,

if the cylinder ID has its axis in the vertical, pro-.

' that if the height of the cylinder is greater than half its diameter the inner reflector I! cannot be given an altitude equal to the length of the cylinder and therefore cannot reflect all the energy emitted from the inner surface of the cylinder and therefore the ratio of altitude to diameterv of the cylinder should have the relation specified. Moreover, it will be seen that best results will be had when this ratio is made as near to one-half, as possible for the following reasons: First, the sound generating area will then. be as large as possible and as a result the sound intensity will be as great as it can be made byincreasing this factor; second, the major diameter of the outer reflector 2| will have its maximum value. Since the concentration of the sound beam is a function of the ratio of the wave length of the sound and the diameter of the generating area, it is advantageous to have this diameter as large as possible. It can be readily demonstrated mathematical- ,ly that the angle of the beam tends to be fixed by the ratio of the velocity of sound in the ma- 1 terial of the cylinder to its velocity in the transmitting medium. The greater the value of this ratio the smaller the spread of the sound beam. We cannot-vary the velocity of sound in the transmitting medium, but we can control to a great extent the velocity in the material of the sound generating element by loading the cylinderin various known manners. The rate of sound propagation in the cylinder cannot well be increased since the magneto-strictive material has about as high a rate of sound transmission as can be found in materials available.

When loaded the resonant frequency of the cylinder is greatly diminished and a smaller dismeter may be used for a desired pitch, which simplifies and cheapens the apparatus. For example, if it be required to produce a fog signal having a pitch. of 200, the diameter of the unloaded cylinder would be about 25.5 feet, but by loading, this dimension can be reduced to a fractional part of the stated size.

If the sound energy from but one surface of I the cylinder is to be used-it can be made of any length independently of its diameter. Fig. 4 shows the nature of the sound field outside a generating cylinder IO. The wavy line 24 represents thewave lengths of the sound generated and the lines 25 indicate the upper and lower boundaries of the sound fleld. The angle shows the; spread oNhe sound beam. It can be shown that the relation between (0), (w) and (h) is approximately as follows:

In which (it) is'the altitude of the cylinder and (in) is the wave length. This relation is similar to that giving the spread of a sound beam generated by a circular diaphragm as will be seen by comparing it with Equation (3). It is evident that the longer the cylinder (the greater the -value of h), the more condensed the sound beam be. In the case of fog signals or simiuses where sound signals are to be spread uniformly about the azimuth, the vertically mounted long cylinder without any reflector very well. A sound generator of this type placed at the focus of a cylindrical mirror between the surface of thecore and the inner wall.

of the cylinder when vibrating radially at its resonantfrequency andthusthe energy is returned to cylinder II in proper phase to be absorbed by the cylinder and to increase the amplitude of vibration thereof. In the instance shown, the spacing between cylinder "and core 30 is three half-wave lengths but it is obvious that it may be any odd number of half-wave lengths.

F'lg. 8 shows schematically an operating assembly in which my present invention may be advantageously used. The coils I around cylinder I! carry a steady polarizing current derived from 9, battery 3|. Secondary coil 32 of a transformer 33 is connected to the terminals of the coils I5 and a condenser 34, preferably variable, is connected across the terminals of coil 32. Primary coil 35 of transformer 33 has one terminal grounded and the other connected to a transfer switch 30, which may be used to connect coil 38 to either a source)? of alternating current or to an amplifier 38 having output connections 39. When the inductance and capacitance of the circuits are such that the circuits resonate to the natural resonant frequency of cylinder II and the frequency of the current derived from source 37 has the same value, the maximum overall efflciency is secured. The condenser 3-6 is utilized to tune the circuits. When switch 88 is connected to source 31, the cylinder It becomes a transmitter of sound energy.

As is well known, if cylinder Ill be acted upon by periodic mechanical forces, a fluctuating volt-, age of the same frequency will be set up in the coils l5 and the device may then be used as a receiver for sound, in which case switch 36 would be connected to amplifler 38 and the output 39 thereof would be connected to .suitable listening or recording devices.

When used as a receiver, the reflector as will direct oncoming plane waves against the outside of cylinder In and reflector l9 willdirect againstthe inner face thereof that portion of the wave entering the cylinder with a phase difference of one-half wave length as compared with the energy imp upon the outer face, whereby all the energy will be additive and produce maximum radial vibration of the cylinder.. It is apparent that this device will very efliciently receive the echoes of its own signals and therefore may be used as a depth finder on ships or as an altitude meter on aircraft. J

It will be understood that the above description and accompanying drawings comprehend only the preferred and general embodiment of my invention, and that various changes in the construction, proportion and arrangement of parts may be made within the scope of the appended claims, without sacriflcing any of the advantages of this invention.

The herein described invention may be manila facturedand used .by or for the Government, of

,4 a the United States of America for governmental purposes without the payment oi! any royalty thereon.

I claim: V

1. In a device of the class described, a hollow magneto-strictive sound-generating and receiving cylinder, positioning means non-rigidly connected to each end of said cylinder, a plurality of coils disposed around said cylinder in substantially toroidal form, each coll passing over a portion of the exterior surface of the cylinder and also over the inner face of the same longitudinal element of the cylinder wall the said coils being of a width between one-fourth.wave length and one-half wave length of the sound emitted bysaid cylinder as measured in the transmitting medium, the distance between any two adjacent coils being substantially equal to the width of a coil, all of said coils being connected together to give an additive magnetic eifect, a sound-reflecting cone disposed within said cylinder, said cone having an apical angle of and an altitude equal to the length of said cylinder, and a frusto-conical sound-reflecting member disposed around said cylinder, said frusto-conical member having an altitudeequal' to the length of said cylinder and a maximum diameter equal to twice the diameter of the said cylinder plus two half wave lengths of the sound in said medium and being spaced from said cylinder at any point a distance one-half wave length greater than the distance of a corresponding point on the inner cone from the cylinder at the same altitude.

2. In a device of the class described, a hollow magneto-strictive sound-generating and receiving cylinder, positioning means non-rigidly connected to each end of said cylinder, a plurality of coils disposed around said cylinder in substantially toroidal form, each coil passing over a portion of the exterior surface of the cylinder, and also over the inner face of the same longitudinal element of the cylinder wall, said coils being of a width between one-fourth wavelength and one-half wave length of the sound emitted by said cylinder as measured in the transmitting medium, the distance between any two adjacent coils being substantially equal to the width of a coil, all of said coils being connected together to give an additive magnetic effect, a sound-reflecting cone disposed within said cylinder, said cone having an apical angle of 90 and an altitude equal to the length of said cylinder, and a frusto-conical soundreflecting member disposed around said cylinder, said irusto-conical member having an altitude equal to the length of said cylinder and a maximum diameter equal to twice the diameter of said cylinder plus two half wave lengths of the sound in said medium and being spaced from said cylinder at any point a distance one-half wave length greater than the distance of a. corresponding point on the inner cone from the cylinder at the same altitude 3. In a devce of the class described, a hollow magneto-strictive sound-generating and receiving cylinder, positioning means non-rigidly connected to each end of said cylinder, means to apply a fluctuating magnetic field to said cylindento cause said cylinder to vibrate radially, a sound-refiecting cone within said cylinder, said cone having an apical angle of 90 and an altitude equal to the length of said cylinder and a frusto-conical;

sound-reflecting member disposed around said cylinder, said frusto-conical sound-reflecting member having an altitude equal to the length or aoosnsi said cylinder and a maximum diameter equal to twice the diameter of said cylinder plus two half wave lengths of sound of the resonant frequency of said cylinder in the transmitting medium and being spaced from said cylinder at any point a distance one-half wave length greater than the I reiiecting cone within said cylinder, said cone having an apical angle of 90 and an altitude equal to the length of said cylinder, 1:. irustoconical sound-reflecting member having an alti-' tude equal to the length of said cylinder and a maximum diameter equal to twice the diameter of said cylinder plus two half wave lengths of sound of the resonant frequency of said cylinder in the transmitting medium and being spaced from said cylinder at any point a distance one- 1 half wave length greaterthan the distance of a corresponding point on the inner cone from thecylinder at the'same altitude and electrical means associated with said cylinder adapted to have a fluctuating voltage set up therein when said cylinder is set into radial mechanical oscillation.

5. -In a device of the class described, a hollow magneto-strictive sound-generating and receiving cylinder, positioning means non-rigidly connected to each end of said cylinder, and a plurality of coils disposed around said cylinder in substantially toroidal form, one side of each coil extending through said cylinder parallel to the axis thereof, said coils being of a width between one-fourth wave length and one-half wave length of the sound emitted by said cylinder as measured in the transmitting medium, the distance between any two adjacent coils being substantially equal to-the width of a coil, and all of said coils being connected together to give an additive magnetic effect.

6. In a device of the class described, a hollow magneto-strictive sound-generating and receiving cylinder, positioning means non-rigidly connected to each end of said cylinder, a plurality of coils disposed around said cylinder in substantially toroidal form, one side of each coil extending through said cylinder parallel to the axis thereof, said coils being of a width between one-fourth wave length and one-half wave length of the sound emitted by said cylinder as measured in the transmitting medium, the distance between any two adjacent coils being substantially equal to the width of a coil, all of said coils being connected together to give an' additive magnetic effect, and means to direct sound waves reaching said device so that the sound waves that reach the inner surface of the said cylinder are opposite in direction and of a phase difference of one-half wave length from the waves reaching the outer surface whereby the effect of the said waves on the two said surfaces is additive to set said cylinder into radial oscillation.

7. In a device of the class described, a hollow magneto-strictive cylinder mounted to be free to execute radial oscillations, a plurality of coils disposed therearound in substantially toroidal form, one side of each-coil extending through said cylinder parallel to the axis thereof, and means to bring into coincidence both as to direction of propagation and as to phase the waves due to 8. In a device of the class described, a hollow cylindrical magneto-strictive member, means to subject said member to a fluctuating magnetic field, and means to bring into coincidence both as to direction of propagation and as to phase the vibrations from both the inner and the outer surface of said member due to such fluctuations.

9. In a device of the class described, a hollow cylinder, means to set said cylinder into radial vibration and means to bring into coincidence both as to direction of propagation .and as to phase waves from both the inner and the outer surface of said\cy-linder.

10. In a device of the class described, a hollow cylinder, means to set said cylinder into radial vibration and means so to change the direction of propagation of waves set unby said cylinder that a disturbance originating at any part of either of the principal surfaces thereof is brought into phase coincidence with the disturbances emanating from every other part of such surfaces.

11. In a device of the class described, a hollow cylinder, means to set said cylinder into radial vibration and means to'cause disturbances set up by such vibration transversely to'the axis of the cylinder to be propagated parallel to the axis of said cylinder and to be brought into phase coincidence.

12. In a device of the class described, a hollow cylinder, means to set said cylinder into radial vibration and means to cause the disturbance set up by a surface of saidcylinder lying parallel to the axis thereof to be propagated in the direction of the length of said cylinder and to bring into phase coincidence in the said direction the disturbances from all parts of said surface.

13. In a device of the class described, a soundgenerating element in the form of a hollow magneto-strictive cylinder, means to set up magneto- V strictive forces in said cylinder to cause it to execute radial vibrations and means to direct the waves set up thereby into a beam in which all parts of a wave front are in the same phase.

14. In a device of the class described, a sound generating and receiving element having two free surfaces and means either to combine the disturbances from both faces into asingle beam in which all parts of a wave front are in the same phase or to cause a portion of an incoming wave to impinge upon the entire area of a surface of said cylinder lying parallel to the axis thereof with all parts of such impinging portion in the same phase.

15. In a device of the class described, a sound receiving element comprising a hollow cylinder of magneto-strictive material, a plurality of coils disposed therearound substantially in the form of a toroid, one side of each of said coils passing through said cylinder parallel'to the axis thereof, means to direct normally against the outer face of said cylinder portions of a plane wave approaching said cylinder and means to direct normally against the inner face of said cylinder that portion of said wave that passes into said cylinder, the energy so directedagainst said inner face being caused to be one-half wave length out of phase with that directed against the portion of the outer face directly opposite thereto.

16. In a device of the class described, 'in combination a sound receiving element comprising a hollow cylinder of magneto-strictive material, a plurality of coils disposed therearound substantially in the form of a toroid, one side of each of said coils passing through said cylinder parallel to the axis thereof, and means to direct against both faces of said cylinder portions of an oncoming plane sound wave, that portion which strikes the inner face of said cylinder being caused'to be one-half wave length out of phase with that which strikes the outer face thereof.

17. In a device of the class described, an acoustic element comprising a hollow cylinder of magneto-strictive material and a plurality of spaced coils disposed therearound in the form of a toroid, one side of each coil extending through said cylinder parallel to the axis thereof the width of the spaces between each two adjacent coilslbeing substantially equal to the width of a coil which is from one-fourth to one-half wave length of sound having the frequency of the natural period. of resonance of the said cylinder.

18. In a device of the class described, a hollow cylindrical magneto-strlctive member, means cooperating therewith to have a fluctuating electric current set up in said means when saidmember executes constrictive and expansive vibrations transversely to the longitudinal axis thereof and means to cause vibrations moving parallel to said axis to impinge upon substantially the entire area of both the inner and outer surfaces of said member with such phase relation that the impulses on the two surfaces are mechanically additive.

19. In a device of the class described, a' hollow inder executes radial vibrations, and means to cause waves travelling parallel to the axis of said cylinder to impinge upon both surfaces thereof with such phase relation as to be mechanically additive.

20. In a device of the class described, a hollow cylinder, means cooperating with said cylinder to have set up in said means a fluctuating electric current when the wall of said cylinder executes radial vibrations and means to cause waves travelling parallel to the axis of said cylinder to impinge upon both surfaces thereof in such manner that the energy impinging upon one surface of said cylinder is 180 degrees out. of phase with the energy impinging upon'the opposite surface thereof.

HARVEY C. HAYES. 

